Runoff Reduction by Four Green Stormwater Infrastructure Systems in a Shared Environment

Green stormwater infrastructure (GI) imitates the hydrology of undeveloped land to mediate the impacts of stormwater runoff, but research is lacking that characterizes the performances of different types of independent GI systems in close proximity to each other in terms of runoff volume reduction. To address this gap, the runoff reduction by four GI systems was monitored for 48 rain events ranging in depth from 2.8 to 96.5 mm, with a total rain depth of 1,404.1 mm from June 2018 to July 2019, during their first full year of operation. The GI systems, located within 1 km of each other along Lorton Road in Fairfax County, Virginia, were a grass channel (GC), bioretention (BR), bioswale (BS), and compost-amended grass channel (CAGC). The GC, BR, and BS were on track to well exceed minimum requirements of the Virginia Department of Environmental Quality, with relative runoff reductions of 78%, 71%, and 56%, respectively, but the CAGC performed near its requirement at 43%. Contrary to expectations, the simply designed GC achieved the highest runoff reduction. The BR, with the second highest runoff reduction, had a small footprint relative to its contributing drainage area and demonstrated the least variation in performance in variable rainfall depths, intensities, and durations. The relatively small volume reductions of the BS and CAGC were attributed to their respective design elements: a sloping underdrain and close proximity to the road. This field study explored variations in runoff volume reductions of the four systems in various rainfall and seasonal conditions with respect to their design complexities, providing insights for future design and implementation of GI. (C) 2021 American Society of Civil Engineers.